Recovery system of heat energy in a fuel cell system

ABSTRACT

A fuel cell system  1  comprises a fuel cell stack  10,  an evaporator  21,  a reforming device  22,  a supercharger  23,  an offgas heating device  24,  and a catalytic combustion chamber  25.  Offgas exhausted from the fuel cell stack  10  is burnt in the catalytic combustion chamber  25,  and the burnt offgas is introduced to the evaporator  21  to be heat exchanged with a reforming raw fuel and reforming air. The burnt offgas cooled by means of the heat exchange is introduced to the offgas heating device  24,  to be used as a heat source for heating the offgas exhausted from the fuel cell stack  10.  The offgas can be heated by the burnt offgas, and the moisture in the offgas can be vaporized and introduced to the catalytic combustion chamber  25.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an energy recovery system for offgasexhausted from a fuel cell in a solid polymer type fuel cell system.

2. Background Art

As one type of fuel cell system, there is one in which an alcohol typefuel, such as methanol and methane, and a hydrocarbon type fuel arereformed into a hydrogen-rich fuel gas by a reforming reactor, and thisfuel gas and an oxidant gas (for example, air) are supplied to a fuelcell to generate power (Japanese Unexamined Patent Application, FirstPublication Nos. Hei 5-290865, Hei 7-192742 and Hei 7-240223).

Moreover, as a fuel cell system using a solid polymer type fuel cell,there is one in which a raw fuel of an alcohol type fuel and ahydrocarbon type fuel, such as methanol and gasoline, is heated by anevaporator to make fuel vapor, this fuel vapor is reformed into ahydrogen-rich fuel gas by a reforming reactor, and this fuel gas and anoxidant gas (for example air) are supplied as a reactant gas to an anodeelectrode side or a cathode electrode side of a fuel cell to generatepower, the anode offgas and the cathode offgas exhausted from the fuelcell are guided to a catalytic combustion chamber to burn hydrogenremaining in the anode offgas, and the heat of the generated combustiongas is used as a heat source for the evaporator to evaporate the rawfuel.

With the solid polymer type fuel cell, adequate humidity is required atthe time of generating power, and therefore in this fuel cell system,the reactant gas is humidified and supplied to the fuel cell. Inaddition, in the fuel cell, at the time of power generation by means ofan electrochemical reaction of hydrogen and oxygen, water is generated,and this water is generated mainly on the cathode electrode side.Therefore, the cathode offgas is exhausted from the fuel cell with highhumidity.

In this fuel cell system, heretofore, the anode offgas and the cathodeoffgas exhausted from the fuel cell are guided directly to the catalyticcombustion chamber and burnt, and the generated combustion gas isdirectly exhausted to the atmosphere, after subjecting to heat-exchangewith the raw fuel in the evaporator.

However, the operating temperature of the solid polymer type fuel cellis about 80°C., and this temperature is approximately the dew-pointtemperature of the cathode offgas. Therefore, if the offgas exhaustedfrom the fuel cell is directly introduced to the catalytic combustionchamber, as described above, the offgas is cooled due to heat radiationalong the offgas piping for guiding the offgas from the fuel cell to thecatalytic combustion chamber. As a result, the moisture in the offgas iscondensed to form water, and this water may be introduced to thecatalytic combustion chamber together with the offgas. In this case, apart of the quantity of heat generated in the catalytic combustionchamber is consumed as latent heat of vaporization of the water. As aresult, there is caused a problem in that the quantity of heat at anadequate temperature level required for evaporating the raw fuel cannotbe supplied to the evaporator.

The present applicant has also developed the following technique andfiled a patent application (not yet published), in order to improve thestarting warm-up in a solid polymer type fuel cell system. This is foraccelerating warm-up of the evaporator, and the construction is suchthat in parallel with the offgas pipe for supplying the offgas to thecatalytic combustion chamber, a starting catalyst warm-up apparatushaving an electric heater catalyst (hereinafter, abbreviated as “EHC”)and a first fuel injection nozzle, and a second fuel injection nozzlewhich directly injects the fuel to the catalytic combustion chamber, areconnected to an upstream portion of the catalytic combustion chamber.

At the time of startup of the fuel cell system, the electric heater ofthe EHC in the starting catalyst warm-up apparatus is energized andheated, and raw fuel (for example, methanol) is injected from the firstfuel injection nozzle to thereby vaporize and bum the raw fuel by theEHC, and the combustion gas is supplied to the catalytic combustionchamber to heat the catalytic combustion chamber. As a result, when thecatalyst in the catalytic combustion chamber is heated to a temperaturehigher than a low activation temperature, the raw fuel is directlyinjected to the surface of the catalyst in the catalytic combustionchamber from the second fuel injection nozzle, and the air forcombustion is supplied to the catalytic combustion chamber via theoffgas pipe, to completely burn the raw fuel injected from the secondfuel injection nozzle in the catalytic combustion chamber, and thecombustion gas is supplied to the evaporator to warm up the evaporator.As a result, early warm-up of the evaporator becomes possible, therebyenabling the fuel vapor to be supplied to the reforming device at anearly stage, and early warm-up of the fuel cell system can be furtherpromoted.

However, in the case where the injected amount of the raw fuel from thesecond fuel injection nozzle is increased for promoting warm-up in thisfuel cell system, the raw fuel such as methanol requires a period forvaporization and temperature rise before combustion. Therefore, the timeuntil reaching the burnt condition is long, and there may be a casewhere the fuel is discharged unburnt from the catalytic combustionchamber. Moreover, since in this case vaporization of the raw fuel isnot sufficient, the raw fuel may be accumulated in the directly upstreamportion of the catalytic combustion chamber, and flow into the catalyticcombustion chamber to cause a hot spot (thermal nonuniformity). Fromsuch a reason, it has been difficult to promote warm-up by increasingthe injection amount of the raw fuel from the second fuel injectionnozzle.

BRIEF SUMMARY OF THE INVENTION

A fuel cell system of the present invention comprises: a solid polymertype fuel cell, to which a reactant gas is supplied to generate power; acombustion chamber which burns offgas exhausted from the fuel cell togenerate a combustion gas; a first heating device which heats an objectto be heated, by using heat of the combustion gas; and a second heatingdevice which provides heat to the offgas by absorbing heat fromcombustion gas exhausted from the first heating device, on an upstreamside of the combustion chamber.

By having such a construction, even if moisture in the offgas exhaustedfrom the fuel cell is cooled and condensed to form condensed water as aresult of heat radiation during the process until reaching thecombustion chamber, this condensed water can be heated by the waste heatof the burnt offgas in the second heating device to thereby effectvaporization. Therefore, the condensed water does not flow directly intothe combustion chamber. As a result, the situation can be preventedwhere a part of the quantity of generated heat in the combustion chamberis consumed by the latent heat of vaporization of water. Thereforethereby a necessary quantity of heat at an appropriate temperature levelcan be supplied to the first heating device.

Moreover, the waste heat in the burnt offgas can be recovered to theoffgas, and the recovered quantity of heat can be added to the heatoutput by the combustion chamber and supplied to the first heatingdevice, thereby enabling promotion of energy saving.

The object to be heated may be raw fuel of the reactant gas, and thefirst heating device may be an evaporator which evaporates the raw fuel.

By having such a construction, it becomes possible to supply thequantity of heat at an appropriate temperature level required forevaporating the raw fuel in a necessary amount required by the fuelcell. It also becomes possible to reduce the consumption of the rawfuel.

The fuel cell system may further comprises: a warm-up air supply devicewhich supplies air for combustion of the combustion chamber from anupstream side of the second heating device, at the time of systemstartup; and a warm-up fuel supply device which supplies warm-up fuel tothe combustion chamber, at the time of system startup.

By having such a construction, the air for combustion supplied from thewarm-up air supply device can be heated by the second heating device,and at the time of startup of the system, the fuel for warm-up suppliedfrom the warm-up fuel supply device can be heated to acceleratevaporization and temperature rise, thereby enabling acceleration ofcombustion of the warm-up fuel. Moreover, the situation can be preventedwhere the warm-up fuel supplied from the warm-up fuel supply device issupplied in an unburnt state to the first heating device. Thereforewastage of the warm-up fuel can be prevented. In particular, when thefirst heating device is an evaporator which evaporates the raw fuel ofthe reactant gas, early warm-up of the evaporator becomes possible, andearly warm-up of the whole fuel cell system also becomes possible.

The combustion chamber may be a catalytic combustion chamber, and theremay be provided a starting catalyst warm-up device which warms up thecatalytic combustion chamber at the time of system startup, and thewarm-up fuel supply device comprises a fuel injection nozzle whichdirectly injects fuel to a catalyst in the catalytic combustion chamber

By having such a construction, the starting catalyst warm-up device canactivate the catalytic combustion chamber immediately after startup ofthe fuel cell system. Moreover, since the warm-up fuel is injected in asprayed state from the fuel injection nozzle, it becomes possible tofurther accelerate vaporization and temperature rise of the warm-upfuel, thereby enabling further reduction of the warm-up time.

The catalytic combustion chamber may comprise a catalytic chamber whichhouses a catalyst and a heating chamber adjacently provided on anupstream side of the catalytic chamber, the second heating device isdirectly connected to the heating chamber, and the starting catalystwarm-up device and a fuel injection nozzle of the warm-up fuel supplydevice may be installed, facing the heating chamber.

By having such a construction, the second heating device and thecatalytic combustion chamber can be arranged in proximity to each other.As a result, at the time of a warm-up operation, vaporization andtemperature rise of the warm-up fuel can be accelerated, therebyenabling further reduction of the warm-up time. Moreover, at the time ofa generating operation, water in the vaporized offgas can be supplied tothe catalytic combustion chamber without being recondensed. Thereforecondensed water can be reliably kept from flowing into the catalyticcombustion chamber.

The starting catalyst warm-up apparatus may comprise an electric heatercatalyst, and a catalyst warm-up fuel injection nozzle which injectsfuel to the electric heater catalyst.

By having such a construction, warm-up of the catalytic combustionchamber at the time of startup can be reliably performed, with a simpleconstruction.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram for a first embodiment of a fuel cell systemaccording to the present invention.

FIG. 2 is a block diagram for a second embodiment of a fuel cell systemaccording to the present invention.

FIG. 3 is a sectional view showing the main part in a third embodimentof a fuel cell system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of a fuel cell system according to the present inventionwill now be described with reference to FIG. 1 to FIG. 3. Each of theembodiment described below are aspects of a fuel cell system mounted ina fuel cell vehicle. However, the present invention is not limited tothe application for vehicles. Furthermore, the present invention is notlimited these embodiments, it is also possible to combine each elementin the following embodiments.

[First Embodiment]

A first embodiment of the fuel cell system according to the presentinvention will first be described with reference to FIG. 1.

FIG. 1 is a block diagram of a fuel cell system 1 with a reformingreactor. The fuel cell system 1 is composed mainly of a fuel cell stack(solid polymer type fuel cell) 10, an evaporator (first heating device)21, a reforming device 22, a supercharger 23, an offgas heating device(second heating device) 24, and a catalytic combustion chamber(combustion chamber) 25.

The fuel cell stack 10 is a solid polymer type fuel cell, and generatespower by an electrochemical reaction of hydrogen in the fuel cellsupplied to an anode electrode 11 side and oxygen in the air as anoxidant gas supplied to a cathode electrode 12 side. In this embodiment,the fuel gas and the air constitute a reactant gas supplied to the fuelcell.

As the fuel gas supplied to the anode electrode 11 side of the fuel cellstack 10, there is used one obtained by reforming a raw fuel to a fuelvapor by the evaporator 21 and then to a hydrogen-rich fuel gas by thereforming device 22.

That is to say, to the evaporator 21, there are supplied a reforming rawfuel obtained by mixing, for example, an alcohol fuel and a hydrocarbonfuel (methanol, gasoline, etc.) and water in a predetermined mixingratio, and the air for reforming. In the evaporator 21, the reformingraw fuel and the reforming air are heated by heat exchange with ahigh-temperature combustion gas supplied from the catalytic combustionchamber 25 in a non-contacting state, and the reforming fuel isevaporated to become a fuel vapor, and is supplied to the reformingdevice 22 from the evaporator 21 via a fuel supply pipe 31, in a stateof being mixed with the heated air.

The reforming device 22 is an auto-thermal type reforming device, whichreacts the fuel vapor with the reforming air to reform it to ahydrogen-rich fuel gas. The reformed fuel gas is supplied to the anodeelectrode 11 side of the fuel cell stack 10 via a fuel gas supply pipe32.

On the other hand, the air supplied to the cathode electrode 12 side ofthe fuel cell stack 10 is humidified by a humidifier (not shown) andsupplied from the supercharger 23 via an air supply pipe 33.

The air supplied to the cathode electrode 12 side of the fuel cell stack10 is used for power generation, and then supplied to the offgas heatingdevice 24, as cathode offgas, via an offgas pipe 34. The fuel gassupplied to the anode electrode 11 side is used for power generation,and then supplied to the offgas heating device 24, as anode offgas, viaan offgas pipe 35 and the offgas pipe 34.

The anode offgas and the cathode offgas (hereinafter, generally referredto as “offgas” in the case where particular discrimination is notnecessary) are heated in the offgas heating device 24, and introduced tothe catalytic combustion chamber 25 via an offgas pipe 36.

The catalytic combustion chamber 25 is for reacting (burning) hydrogenremaining in the anode offgas and oxygen remaining in the cathodeoffgas, and the burnt offgas, having reached a high temperature due tothis reaction, is supplied to the evaporator 21 via an offgas pipe 37,as a heat source for heating the reforming raw fuel and the reformingair.

The burnt offgas cooled by means of heat exchange with the reforming rawfuel and the reforming air in the evaporator 21 is supplied to theoffgas heating device 24, as a heat source for heating the offgasexhausted from the fuel cell stack 10, via an offgas pipe 38, and thendischarged to the atmosphere as exhaust gas.

Moreover, along the fuel gas supply pipe 32, there is provided athree-way switchover valve 40, and this three-way switchover valve 40 isconnected to the offgas pipe 35 via a by-pass pipe 41. The three-wayswitchover valve 40 is a switchover valve for enabling selectiveconnection of a fuel gas supply pipe 32 a on the upstream side of thisthree-way switchover valve 40 either to a fuel gas supply pipe 32 b onthe downstream side or the by-pass pipe 41. The three-way switchovervalve 40 controls the switchover such that until warm-up of thereforming device 22 is completed, the gas sent out from the reformingdevice 22 is made to flow to the by-pass pipe 41 so as to by-pass thefuel cell stack 10, and after completion of warm-up of the reformingdevice 22, the gas sent out from the reforming device 22 is made to flowto the fuel cell stack 10.

Next, the operation of this fuel cell system 10 will be described.

At the time of a generating operation when the fuel cell stack 10generates power, the burnt offgas introduced from the catalyticcombustion chamber 25 to the evaporator 21 is cooled to 200 to 300° C.by means of heat exchange with the reforming raw fuel and the reformingair in the evaporator 21, and exhausted from the evaporator 21, andsupplied as a heat source to the offgas heating device 24 via the offgaspipe 38.

On the other hand, as described above, the humidity of the offgas,particularly of the cathode offgas exhausted during power generation bythe fuel cell stack 10, being a solid polymer type fuel cell, is veryhigh, and the operating temperature of the fuel cell stack 10 is about80° C. being around the dew point temperature of the cathode offgas.Moreover, this offgas is introduced to the offgas heating device 24 at atemperature of from 60 to 90° C.

As a result, in the offgas heating device 24, the offgas is heated toabout 150 to 250° C. by means of heat exchange with the burnt offgas ofa temperature of about 200 to 300° C. Therefore, even if moisture in theoffgas is condensed to generate condensed water while the offgas flowsfrom the fuel cell stack 10 to the offgas heating device 24, thiscondensed water can be completely vaporized in the offgas heating device24. As a result, the condensed water can be prevented from flowing intothe catalytic combustion chamber 25.

Accordingly, a part of the quantity of generated heat is not consumed inthe catalytic combustion chamber 25 due to the latent heat ofvaporization of water. Therefore it becomes possible to generate thequantity of heat at an appropriate temperature level necessary forevaporation of the raw fuel in the catalytic combustion chamber 25, andsupply this to the evaporator 21.

Moreover, the burnt offgas exhausted from the evaporator 21 has beenheretofore simply exhausted. However, in this fuel cell system 1, thewaste heat in the burnt offgas is recovered to the offgas, and therecovered heat is added to the combustion heat of the catalyticcombustion chamber 25, and then supplied to the evaporator 21. Thereforethe energy recovery increases, and energy saving is promoted.

For example, when compared to the case where the offgas heating device24 is not provided and heat and calories for the same temperature levelare supplied to the evaporator 21, in the case where the offgas heatingdevice 24 is provided, the feed rate of the anode offgas to thecatalytic combustion chamber 25 can be reduced by 30 to 40%. That is,the fuel can be reduced.

[Second Embodiment]

Next, a second embodiment of the fuel cell system according to thepresent invention will be described with reference to FIG. 2. The pointthat is different in the fuel cell system 1 of the second embodiment tothat of the first embodiment is as follows.

The catalytic combustion chamber 25 has a catalyst chamber 25 a foraccommodating the catalyst, and a heating chamber 25 b provided on theupstream side of the catalyst chamber 25 a, and the end of thedownstream side of the offgas pipe 36 is connected to this heatingchamber 25 b.

Moreover, to the heating chamber 25 b, there are connected towards(facing) the heating chamber 25 b, a starting catalyst warm-up apparatus(starting catalyst warm-up device) 50 comprising an electric heatercatalyst (hereinafter referred to as EHC) 51 and a first fuel injectionnozzle (fuel injection nozzle for warming up the catalyst) 52 forinjecting raw fuel and air to this EHC 51, and a second fuel injectionnozzle (warm-up fuel supply device) 53 for injecting raw fuel directlyto the catalyst chamber 25 a of the catalytic combustion chamber 25. Thestarting catalyst warm-up apparatus 50 and the second fuel injectionnozzle 53 are arranged in parallel with each other with respect to theoffgas pipe 36. The raw fuel same as the raw fuel supplied to theevaporator 21 can be supplied to the first fuel injection nozzle 52 andthe second fuel injection nozzle 53.

In this fuel cell system 1 of the second embodiment, an air supply pipe33 and an offgas pipe 34 are connected by an air by-pass pipe 42, and acontrol valve 43 is provided along the air by-pass pipe 42. In thisembodiment, a supercharger 23, the air by-pass pipe 42 and the controlvalve 43 constitute a warm-up air supply device for supplying the airfor combustion of the catalytic combustion chamber 25 from the upstreamside of the offgas heating device 24 (second heating device), at thetime of startup of the system.

Other construction is the same as that of the first embodiment, and thesame parts are denoted by the same reference symbols, and thedescription thereof is omitted.

Next, the operation of the fuel cell system 1 in this second embodimentwill be described.

The fuel cell system 1 is automatically driven as described below, by acontrol unit for controlling the fuel cell (not shown) (hereinafter,abbreviated as “FCECU”).

At first, the FCECU energizes the electric heater of the EHC 51 by anoperation start signal of the fuel cell system 1, to heat the catalystof the EHC 51, and injects the raw fuel and the air from the first fuelinjection nozzle 52 to vaporize this raw fuel by the EHC 51, and effectcatalytic combustion. Then, the combustion gas is supplied to thecatalyst chamber 25 a via the heating chamber 25 b to heat the catalystin the catalytic combustion chamber 25, to thereby warm up the catalyst.Accordingly, with the fuel cell system 1 in this second embodiment,warm-up of the catalytic combustion chamber 25 is performed withoutwaiting for completion of warm-up of the offgas heating device 24. Atthis point of time, the three-way switchover valve 40 makes the fuel gassupply pipe 32 a communicate with the by-pass pipe 41, and shuts off thefuel gas supply pipe 32 b. Also, the raw fuel and the reforming air arenot supplied to the evaporator 21.

In this manner, the catalytic combustion chamber 25 is warmed up, andwhen the catalyst in the catalytic combustion chamber 25 reaches the lowactivation temperature, injection of the raw fuel from the first fuelinjection nozzle 52 is stopped, and the raw fuel is injected from thesecond fuel injection nozzle 53, to blow the fuel directly onto thesurface of the catalyst in the catalyst chamber 25 a through the heatingchamber 25 b. Also, by opening the control valve 43, the air forcombustion is supplied to the catalytic combustion chamber 25 via theoffgas pipe 34, the offgas heating device 24 and the offgas pipe 36. Atthe same time, the reforming air is supplied to the evaporator 21. Atthis point of time, the reforming raw fuel has not yet been supplied tothe evaporator 21. Moreover, the three-way switchover valve 40 remainsin the previous state, so that the gas sent out from the reformingdevice 22 is made to flow to the by-pass pipe 41.

As a result, the raw fuel injected from the second fuel injection nozzle53 to the catalytic combustion chamber 25 is completely burnt in thecatalytic combustion chamber 25, together with the air for combustionsupplied from the supercharger 23. The generated high-temperaturecombustion gas is supplied to the offgas heating device 24 via theevaporator 21 and the offgas pipe 38, for warming up the offgas heatingdevice 24. With progress of warm-up of the offgas heating device 24,heat exchange progresses between the combustion gas and the air forcombustion at a normal temperature supplied from the supercharger 23, tothereby heat the air for combustion. The heated air for combustion issupplied to the heating chamber 25 b of the catalytic combustion chamber25, where the raw fuel injected from the second fuel injection nozzle 53is heated.

In this manner, when the air for combustion supplied from thesupercharger 23 is heated, the quantity of heat recovered from thecombustion gas in the offgas heating device 24 is added to the heatoutput of the raw fuel in the catalytic combustion chamber 25, to besupplied to the evaporator 21. Therefore, the warm-up time of theevaporator 21 is reduced.

Moreover, when the raw fuel injected from the second fuel injectionnozzle 53 is heated in this manner, vaporization and temperature rise ofthe raw fuel injected from the second fuel injection nozzle 53 isaccelerated. Therefore, even in the case where the injection quantity ofthe raw fuel from the second fuel injection nozzle 53 is increased,liquid raw fuel is not accumulated immediately on the upstream side ofthe catalyst in the catalytic combustion chamber 25. Also, the timeuntil the raw fuel injected from the catalytic combustion chamber 25reaches the burnt condition is reduced, and unburnt raw fuel is notdischarged from the catalytic combustion chamber 25. Therefore completecombustion becomes possible in the catalytic combustion chamber 25.Furthermore, since vaporization of the raw fuel is accelerated, the rawfuel in the catalyst chamber 25 a can be well dispersed, thereby makingit difficult for hot spots to occur in the catalyst in the catalyticcombustion chamber 25.

Furthermore, even when warm-up of the evaporator 21 is performed asdescribed above, the reforming air is heated by the combustion gasexhausted from the catalytic combustion chamber 25, in the evaporator21. Then, the heated reforming air is introduced to the offgas pipe 34through the reforming device 22, the fuel gas supply pipe 32 a, theby-pass pipe 41 and the offgas pipe 35, where it is joined with the airfor combustion supplied from the supercharger 23. On the other hand, thecombustion gas having heated the reforming air is introduced to theoffgas heating device 24 from the evaporator 21 through the offgas pipe38, and then exhausted.

When the reforming air exhausted from the evaporator 21 reaches apredetermined temperature, supply of the reforming raw fuel to theevaporator 21 is started, to continue the warm-up operation of theevaporator 21. When the vapor temperature of the reforming raw fuel sentout from the evaporator 21 reaches a temperature at which this can besupplied to the reforming device 22, injection of the raw fuel from thesecond fuel injection nozzle 53 is stopped to complete warm-up of theevaporator 21, and subsequently operation shifts to the warm-upoperation of the reforming device 22. When warm-up of the reformingdevice 22 is completed, the three-way switchover valve 40 shuts off theby-pass pipe 41, to make the fuel gas supply pipes 32 a and 32 bcommunicate with each other, and the control valve 43 is then shut. As aresult, the fuel gas reformed by the reforming device 22 is supplied tothe anode electrode 11 side, and air is supplied to the cathodeelectrode 12 side, of the fuel cell stack 10, so that the fuel cellstack 10 can generate power.

After the fuel cell stack 10 attains a state capable of generatingpower, the same operation and effects as those of the fuel cell system 1in the first embodiment described above are exhibited in the fuel cellsystem 1 in this second embodiment.

In this manner, in the fuel cell system 1 in this second embodiment, inaddition to the operation and effects of the fuel cell system 1 in thefirst embodiment, early warm-up of the evaporator 21 becomes possible.As a result, the fuel vapor can be supplied to the reforming device 22earlier, to accelerate warm-up of the reforming device 22, therebyenabling acceleration of early warm-up of the fuel cell system 1.

[Third Embodiment]

A third embodiment of the fuel cell system according to the presentinvention will now be described with reference to FIG. 3. The thirdembodiment can be said to be a variation example of the fuel cell system1 in the second embodiment, and can also be said to be a more specificconfiguration example.

FIG. 3 is a sectional view showing the vicinity of an offgas heatingdevice 24 and a heating chamber 25 b of a catalytic combustion chamber25, in the fuel cell system 1 in the third embodiment.

The offgas heating device 24 is a stacked heat exchanger, wherein aplurality of passages 24 a where the burnt offgas exhausted from theevaporator 21 circulates, is laminated on each other with a space, andthe burnt offgas exhausted from the fuel cell stack 10 circulatesbetween these passages 24 a.

The heating chamber 25 b of the catalytic combustion chamber 25 isdirectly connected to this offgas heating device 24, and therefore, inthe case of this third embodiment, the offgas pipe 36 in the secondembodiment is not provided.

On one side on the outer periphery of the heating chamber 25 b, there isadjacently provided a startup combustion gas chamber 54 of the startingcatalyst warm-up apparatus 50, so that the heating chamber 25 b and thestartup combustion gas chamber 54 are communicated with each other. Thatis to say, the startup combustion gas chamber 54 of the startingcatalyst warm-up apparatus 50 is provided facing the heating chamber 25b. An EHC chamber 55 is provided adjacent to the startup combustion gaschamber 54, and an EHC 51 is housed in the EHC chamber 55. Moreover, afirst fuel injection nozzle 52 is installed in an upper end portion ofthe EHC chamber 55.

The raw fuel and air injected from the first fuel injection nozzle 52are injected to the EHC 51 in the EHC chamber 55, and catalyticallycombusted in the EHC 51. The combustion gas flows out from the EHCchamber 55 to the startup combustion gas chamber 54, and further to theheating chamber 25 b via a continuous hole 54 a, and is then introducedinto a catalyst chamber 25 a.

On an other side on the outer periphery of the heating chamber 25 b,there is installed a second fuel injection nozzle 53 so that the fuelcan be directly injected to the catalyst in the catalyst chamber 25 a ofthe catalytic combustion chamber 25. That is, the second fuel injectionnozzle 53 is provided so as to face the heating chamber 25 b.

In this third embodiment, by setting the length in the gas flowingdirection of the heating chamber 25 b as small as possible, the offgasheating device 24 and the catalyst chamber 25 a of the catalyticcombustion chamber 25 can be arranged in close proximity to each other,and the quantity of heat of the air for combustion or the offgas, heatedby the offgas heating device 24 can be supplied to the catalyticcombustion chamber 25 without decreasing the quantity thereof.

Accordingly, at the time of warm-up operation of the fuel cell system 1,vaporization and temperature rise of the fuel injected from the secondfuel injection nozzle 53 can be further accelerated, thereby enablingfurther reduction in the warm-up time.

Moreover, at the time of power generation of the fuel cell system 1,after the moisture in the offgas is vaporized by the offgas heatingdevice 24, the vaporized moisture can be supplied to the catalyticcombustion chamber 25 in the gaseous state, without re-condensing thevaporized moisture.

Other construction is the same as that of the second embodiment.

What is claimed is:
 1. A fuel cell system comprising: a solid polymertype fuel cell, to which a reactant gas is supplied to generate power; acombustion chamber which burns offgas exhausted from said fuel cell togenerate a combustion gas; a first heating device which heats an objectto be heated, by using heat of said combustion gas; and a second heatingdevice which provides heat to said offgas by absorbing heat fromcombustion gas exhausted from said first heating device, on an upstreamside of said combustion chamber.
 2. A fuel cell system according toclaim 1, wherein said object to be heated is raw fuel of said reactantgas, and said first heating device is an evaporator which evaporatessaid raw fuel.
 3. A fuel cell system according to claim 2, furthercomprising a switchover valve which selects one of a first passagetransmitting reactant gas heated by said first heating device to saidsolid polymer type fuel cell, and a second passage transmitting saidreactant gas heated by said first heating device to said second heatingdevice.
 4. A fuel cell system according to claim 2, further comprising areforming device which reforms said raw fuel heated by said firstheating device to a hydrogen-rich fuel gas.
 5. A fuel cell systemaccording to claim 1, further comprising: a warm-up air supply devicewhich supplies air for combustion of said combustion chamber from anupstream side of said second heating device, at the time of systemstartup; and a warm-up fuel supply device which supplies warm-up fuel tosaid combustion chamber, at the time of system startup.
 6. A fuel cellsystem according to claim 5, wherein said combustion chamber is acatalytic combustion chamber, and there is provided a starting catalystwarm-up device which warms up said catalytic combustion chamber at thetime of system startup, and said warm-up fuel supply device comprises afuel injection nozzle which directly injects fuel to a catalyst in saidcatalytic combustion chamber.
 7. A fuel cell system according to claim6, wherein said catalytic combustion chamber comprises a catalyticchamber for housing a catalyst and a heating chamber adjacently providedon an upstream side of said catalytic chamber, said second heatingdevice is directly connected to said heating chamber, and said startingcatalyst warm-up device and said fuel injection nozzle of said warm-upfuel supply device are installed, facing said heating chamber.
 8. A fuelcell system according to claim 6, wherein said starting catalyst warm-upapparatus comprises an electric heater catalyst, and a catalyst warm-upfuel injection nozzle which injects fuel to said electric heatercatalyst.
 9. A fuel cell system according to claim 5, wherein saidwarm-up fuel supply device comprises a supercharger which supplies airto said solid polymer type fuel cell and a bypass valve which can supplyair from said supercharger to said second heating device.